A fuel cell is a device producing electricity through a reaction between oxygen and a fuel such as hydrogen, natural gas or the like. Fuel cells are characterized by high efficiency, non-polluting and noise-free characteristics, and the like, which are thus regarded as future energy technology.
Solid oxide fuel cells (SOFC) may utilize a solid oxide as an electrolyte allowing oxygen ions to pass therethrough, and zirconium oxide (ZrO2), cerium oxide (CeO2), lanthanum strontium gadolinium magnesium (LSGM) or the like may be used as the electrolyte material.
The electrolyte may contain a stabilizer such as yttria (Y2O3) ceria (CeO2), scandia (Sc2O3), gadolinia (Gd2O3) or the like in order to improve ionic conductivity and thermal stability at high temperatures.
A unit cell of the SOFC may be manufactured by arranging the solid electrolyte to have one side attached to an anode material and the other side attached to a cathode material. A mixture of a nickel oxide (NiO) and yttria stabilized zirconia (YSZ) is commonly used as an ande material, and lanthanum strontium manganite (LSM), lanthanum strontium cobalt ferrite (LSCF) or the like is commonly used as a cathode material.
In recent years, it has been found that the electrochemical properties of fuel cells can be improved by using LSCF as the cathode material, rather than LSM. Accordingly, the development and evaluation of LSCF as the cathode material has been actively promoted.
However, such an LSCF cathode material may react with the zirconia-based (ZrO2) electrolyte material, thereby forming a composite oxide having low ionic conductivity, such as lanthanum zirconate (La2Zr2O7) or strontium zirconate (SrZrO3), on an interface between the cathode and the electrolyte while the cathode is sintered and the fuel cell is operated at high temperatures.
Such a compound may decrease a diffusion rate of oxygen ions formed at cathode through the electrolyte to react with hydrogen in the anode, thereby degrading the overall performance of the fuel cell.
Therefore, in order to obtain durability and reliability of the fuel cell, it is necessary to prevent a reaction between two layers, one of which is formed of LSCF as the cathode material and the other one is formed of a zirconia-based (ZrO2) material as the electrolyte material.